This invention relates to a movement distance detector for detecting the amount of movement of an object.
Various such movement distance detectors have been proposed.
For example, a movement distance detector disclosed in Unexamined Japanese Patent Publication 2-302611 is used to measure the movement of an automotive brake pedal.
This movement distance detector has a piston supported in a cylinder through a first compression spring and coupled to a brake pedal through a second compression spring. The first compression spring is more rigid than the second one, so that the pedal stroke applied to the piston through the second compression spring is shortened by the more rigid first compression spring. The thus shortened stroke pedal is detected by a detector. In other words, the relatively large pedal stroke is detected by measuring the shortened stroke of the piston.
In this arrangement, since the pedal stroke is detected in the form of shortened stroke of the piston, the resolution of detection is poor. Also, since springs are used to shorten stroke, responsiveness is not good.
Also in this arrangement, the detection accuracy is determined by the rigidity ratio between the first and second compression springs. Thus, it is difficult to adjust the accuracy with high reproducibility. Also, spring rigidities tend to change with time. This can cause detection errors.
A suspension stroke sensor disclosed in Unexamined Japanese Utility Model Publication 2-82604 is free of these problems. It has a sheath member mounted on a piston rod of a cylindrical shock absorber and having an outer periphery tapered in the axial direction of the piston rod. A gap sensor which utilizes high-frequency induction or electrostatic induction is mounted on the cylinder opposite the tapered surface of the sheath member so that the distance between the tapered surface of the sheath member and the gap sensor will change linearly with the piston stroke. Since this distance is directly converted into the stroke of the piston rod, the stroke can be detected with high response, accuracy and reproducibility. Also, measured values are less likely to change with time.
The detection accuracy of this suspension stroke sensor depends largely upon the dimensional accuracy of the sheath member. Thus, the sheath member has to be machined with a high degree of accuracy. This results in a rather high production cost of the entire device.
An object of this invention is to provide a movement distance detector which is simple in structure and thus can be manufactured at low cost, which can detect the movement of an object with high responsiveness, accuracy and reproducibility and which will maintain high levels of performance over time.